A(1). Field of the Invention
The invention relates to an arrangement for converting start-stop signals into an isochronous signal, comprising an elastic store wherein the sampling values obtained by sampling the start-stop signal at sampling moments, which have a given position with respect to given signal transitions, are stored in the elastic store and wherein the sampling values are read consecutively from the elastic store at isochronous instants for forming the isochronous signal.
The invention stems from the field of time-division multiplexing of telex signals in accordance with CCITT-recommendation R101.
In these multiplex telegraphy systems each telex signal is converted into an isochronous bit stream having one bit per signal element and the isochronous bit streams are interleaved bit-wise to an aggregate signal having a bit rate of 2400 bit/sec.
A(2). Description of the Prior Art
U.K. Pat. No. 1,065,866 discloses a system for converting a start-stop signal into an isochronous signal.
This system comprises a shift register having two register stages. Samples of the telegraph signal are applied to the input of the first register stage and the isochronous signal is obtained from the output of the second register stage. Shifting the information from the first register stage to the second register stage is controlled by a register which registers whether an information has been read from the second register stage and a new sample has been entered in the first stage. If these conditions have been satisfied, a shift pulse is applied to the shift register to shift the information from the first to the second register stage.
This shift register with associated control forms an elastic store by means of which differences in speed between the incoming telegraphy signal and the outgoing isochronous signal can be equalised by shortening or extending the stop elements of the telegraphy characters. In accordance with CCITT-recommendation R101 the isochronous rate is 2% higher than the nominal rate of the telegraphy signal and the difference in rate will be compensated for by extending the stop elements.